Test dates: 11-13 August 1997
Oregon State University personnel:
Stephen Pierce, and Andy Dale
National Park Service Crater Lake
Research Team: Scott Girdner, Jeff Milder, and Ashley Gibson
Objectives: Test new Wide Area Differential GPS (WADGPS) surface
drifters and examine Crater Lake circulation.
We have implemented WADGPS on a surface drifter. WADGPS is a technique to
improve GPS positioning accuracy from +/-100 m to +/- 20 m or better. See Wilson et al.
(1996) for technical details. This Crater Lake work was the "full field
test" mentioned in the Wilson et al. paper, planned for August 1996 but delayed
until August 1997.
T.C. Wilson, J.A. Barth, S.D. Pierce, P.M. Kosro, and B.W. Waldorf, "A
Lagrangian drifter with inexpensive wide area differential GPS positioning,"
Oceans '96 MTS/IEEE Conference Proceedings, 2, 851-856, 1996.
Future plans: Plot up wind records (we have these in hand) and
interpret drifter motions in terms of simple closed-basin, wind-forced
|Figure 1. One
drifter tracked over 18 hours with a fix every 5 min. Note improvements in
positions and speed estimates using WADGPS.
Drifter location and speed vs. time for all four drifters over repeated
deployments. Maximum speed observed is ~30 cm/s, surprisingly large.
Drifter tracks in eastern half of Crater Lake. Triangles mark deployment
locations; marks every half-hour give indication of speed. Note
counter-clockwise circulation in eastern basin.
Drifter tracks color-coded by speed. Strong southward flow in mid-lake and
intermittently strong "ram" current on eastern side.